Viscosifier, its uses, and its manufacture

ABSTRACT

A composition of matter suitable for increasing the viscosity of liquids comprises tendrillar carbonaceous material (TCM) having a ultra low bulk density of less than about 0.1 g/cm 3  and comprises intertwined tendrils having a diameter (number average) of from about 0.05 to about 0.2 micron and a length (number average) to diameter (number average) ratio greater than about 10, the tendrils comprising carbon fibers and an iron metal component dispersed throughout the carbon fibers as nodules that are intimately associated with and at least partially bonded to the carbon fibers, the tendrillar carbonaceous material comprising from about 0.1 to about 5% by weight iron. The TCM can be used as a viscosifier and for suspending solids in such applications as drilling muds, lubricating oils and greases. The TCM can be prepared by disproportionating carbon monoxide in the presence of iron contained in a blend of (1) previously formed TCM and (2) iron containing particles.

CROSS-REFERENCES

This is a division of application Ser. No. 738,203 filed May 24, 1985now U.S. Pat. No. 4,689,161.

This application is related to application Ser. No. 620,996 filed onJune 15, 1984 now U.S. Pat. No. 4,650,657 by Edward F. Brooks, entitled"Method for Making Carbonaceous Materials", which is acontinuation-in-part of application Ser. No. 339,778 filed on Jan. 15,1980 by Edward F. Brooks, now abandoned, which is a continuation ofapplication Ser. No. 188,201 filed on Sept. 18, 1980 by Edward F.Brooks, now abandoned. These three patent applications are incorporatedherein by this reference.

BACKGROUND

The present invention relates to a viscosifier, its uses, and methodsfor its manufacture.

Viscosifiers for thickening or gelling organic and aqueous liquids havemany applications. These include lubricating oils, greases, and drillingfluids. Exemplary of viscosifiers used are: (1) linear polymers forimproving the viscosity-index of lubricating oils; (2) fatty acid soapsof lithium, calcium, sodium, aluminum, and barium, and clays which areused in greases; and (3) clays such as bentonite in drilling fluids. Indrilling fluids clays act as viscosifiers, and also act to suspendweighting materials such as barite in the fluid.

Many viscosifiers have significant limitations, including inadequatethermal stability, inability to be used both with aqueous andhydrocarbon based fluids, limited use with acidic and/or basic liquids,inadequate shear thinning properties, incompatibility with electrolytes,and inability to adequately suspend weighting materials such as barites.

Accordingly, for many applications there is a need for an improvedviscosifier.

SUMMARY

The present invention is directed to a viscosifier that satisfies thisneed. According to the present invention a composition of mattersuitable for increasing the viscosity of liquids comprises ultra lowbulk density tendrillar carbonaceous material having a bulk density ofless than 0.1 g/cm³ and generally a surface area of less than about 190m² /g and comprising intertwined tendrils having a diameter (numberaverage) of from about 0.05 to about 0.2 micron, and a length (numberaverage) to diameter (number average) ratio greater than about 10. Asused herein, by "TCM" there is meant the novel low bulk density materialof the present invention. All bulk densities of TCM presented hereinrefer to the bulk density of TCM "as prepared".

Preferably the TCM has a bulk density of less than about 0.05 g/cm³ andthe tendrils comprise carbon fibers with an iron metal componentdispersed throughout the carbon fibers as nodules that are intimatelyassociated with and at least partially bonded to the carbon fibers. TheTCM can comprise from about 0.1 to about 5% by weight iron, preferablyless than about 4% by weight iron, about 93.5 to about 99.9% by weightcarbon, and up to about 1.5% by weight hydrogen. Generally the TCM has abulk density of at least about 0.02 g/cm³. Preferably the TCM has asurface area of less than about 160 m² /g and generally greater thanabout 30 m² /g. The tendrils preferably have a diameter (number average)of from about 0.08 to about 0.14 micron.

TCM can be added to a liquid to increase the viscosity of the liquid.Typically sufficient TCM is added to liquid, in an amount of at least0.1% by weight, that the viscosity of the liquid at a shear rate of 1sec⁻¹ is at least 10 cp and at least a factor of 10 greater than theviscosity of the liquid without the TCM present. TCM can also be addedto a liquid to suspend dense solids in the liquid. By the term "densesolid" there is meant a solid having a density greater than the densityof the liquid in which the solid is dispersed.

TCM is effective as a viscosifier for both aqueous and hydrocarbonliquids, and including emulsions such as water-in-oil emulsions. It iseffective as a viscosifier for acidic solutions such as solutions havinga pH of less than 4, and for basic solutions, such as solutions having apH of greater than 9.

TCM can be used in drilling fluids. A drilling fluid can comprise aliquid having dispersed therein (i) sufficient weighting agent such asbarite that the drilling fluid has a density of at least 1.1 g/cm³ and(ii) sufficient TCM in an amount of at least 0.1% by weight based on theweight of the drilling fluid that the drilling fluid has a viscosity ofat least 10 cp at a shear rate of 1000 sec⁻¹. The liquid in the drillingfluid can be water, an oil-in-water emulsion, or a hydrocarbon. Thetendrillar carbonaceous material not only increases the viscosity of thedrilling fluid but also helps suspend the weighting agent. The drillingfluid can include components typically found in drilling fluids such as(1) other viscosity increasing agents such as clay, (2) viscositythinning agents, (3) alkalinity control agents to maintain the pH of thedrilling fluid greater than 7.0, (4) surfactants, and/or (5)flocculents.

A grease can comprise a lubricating oil having dispersed thereinsufficient TCM, in an amount of at least 0.1% by weight of the grease,that the grease has an apparent viscosity of at least 4 Pa·S at a shearrate of 100 sec⁻¹. A grease generally contains from about 5 to about 15%by weight TCM. The grease can also contain, in addition to the TCM,conventional gelling agents such as those selected from the groupconsisting of fatty-acid soaps of lithium, calcium, sodium, aluminum,and barium.

A method for increasing the viscosity of a liquid according to thepresent invention merely requires dispersing TCM in the liquid, such asby adding TCM to the liquid and then mixing. Generally no wetting agentis required.

A method for suspending a dense solid in a liquid according to thepresent invention merely requires dispersing the TCM in the liquid,before, during, or after adding the dense solid.

This invention includes two novel methods for preparing TCM. Bothmethods require an initial feed of TCM which can be prepared by atechnique described below. One of the novel methods uses a fixed bedreactor and the other method uses a fluidized bed reactor. In the fixedbed method, previously formed feed TCM is blended with a finely dividedparticulate comprising iron, where the blend contains at least about 5%by weight iron, preferably less than about 60% by weight iron. A feedgas containing carbon monoxide is introduced into a reaction zone havinga fixed bed of the blend. The iron of the particulate catalyzes thedisproportionation of at least a portion of the carbon monoxide to formadditional TCM. The temperature in the reaction zone is maintained atfrom about 400° to about 500° C. The additional TCM is recovered fromthe reaction zone.

Preferably the finely divided particulate has a number average diameterof less than 10 microns. The iron in the particulate can be selectedfrom the group consisting of oxides of iron, elemental iron, andcombinations thereof.

In the fluidized bed method, feed TCM is also blended with the finelydivided particulate comprising iron compounds, the blend containing fromabout 5 to about 40% by weight iron, preferably less than about 20% byweight iron. Feed gas containing carbon monoxide is introduced into areaction zone having a bed containing the blend to form a fluidized bed.Preferably the feed gas is introduced at a superficial velocity of fromabout 3 to about 20 cm/sec, and more preferably from about 6 to about 15cm/sec. In the fluidized bed the iron of the particulate catalyzes thedisproportionation of at least a portion of the carbon monoxide to formadditional TCM. The temperature in the reaction zone is maintained fromabout 400° to about 500° C., and additional TCM formed in the reactionzone is recovered therefrom. Preferably the temperature in the fixed bedreaction zone is from about 430° to about 460° C. and in the fluidizedbed reaction zone is from about 450° to about 490° C.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a transmission electron micrograph at 32,000 magnification ofTCM having a bulk density of about 0.03 g/cm³, a surface area of about130 m² /g, and an iron content of about 3% by weight;

FIG. 2 is a scanning electron microscope photograph of TCM produced withiron oxide powdered catalyst at a magnification of 20,000, the TCMhaving a bulk density of about 0.027 g/cm³, a surface area of about 122m² /g, and an iron content of about 4.2% by weight;

FIG. 3 is a plot of surface area versus bulk density for typical TCM;

FIG. 4 is a plot of the viscosity of mineral oil containing 5% by weightTCM versus the surface area of the TCM;

FIG. 5 presents plots of viscosity versus shear rate for mineral oilcontaining 5% by weight TCM and for pure mineral oil at severaltemperatures;

FIG. 6 presents plots of viscosity as a function of carbon loading formineral oil containing various forms of carbon including TCM;

FIG. 7 presents plots of viscosity versus shear rate for mineral oilloaded with various forms of carbon including TCM;

FIG. 8 presents plots of viscosity versus shear rate for a water basedmud, aged at 300° F., containing barite and/or TCM; and

FIG. 9 presents plots of viscosity versus shear rate for an oil basedmud containing (a) TCM or (b) TCM and barite.

DESCRIPTION A. Physical Properties and Composition of TCM

It has been discovered that certain carbon containing materials ofexceptionally low bulk density are remarkably effective viscosifiers.These carbon containing materials are produced by novel processes andmust have specific physical properties to be effective. This material istendrillar carbonaceous material, i.e., TCM. It comprises intertwinedtendrils comprising carbon.

For the TCM to be an effective viscosifier, it must have a bulk densityof less than about 0.1 g/cm³, and preferably a bulk density of less thanabout 0.05 g/cm³. Generally TCM has a bulk density of at least about0.02 g/cm³. The importance of the TCM having a bulk density of less thanabout 0.1 g/cm³ is demonstrated by Example 11 below.

By "bulk density" of TCM there is meant the bulk density of the "asprepared" material, prior to any further processing. It is possible tochange the density of "as prepared" TCM by processes such as compactingTCM or by dispersing TCM in a liquid and then drying the TCM.

All bulk density values presented herein are values determined by thefollowing technique. A tared 25 ml graduated cylinder is filled with asample of the TCM. The bottom of the cylinder is gently tapped on a flatsurface while the cylinder is slowly rotated. This procedure iscontinued until no further change in sample volume occurs. The cylinderand sample are then weighed and the sample bulk density is calculated asthe weight of the sample divided by the final volume that the sampleoccupied in the graduated cylinder. For a given sample of material, thevalues obtained are generally reproducible within ±5%.

In preferred methods for producing TCM as described in detail below, theTCM is formed by the disproportionation of a feed gas such as a gascontaining carbon monoxide over an iron containing catalyst. The TCMproduced by this technique has tendrils comprising carbon fibers and aniron metal component dispersed throughout the carbon fibers as nodulesthat are intimately associated with and at least partially bonded to thecarbon fibers.

TCM contains no more than about 5% by weight iron, and preferably lessthan about 4% by weight iron. Higher iron contents result in shortertendrils which results in significantly reduced viscosifying effects inliquids as demonstrated by Example 12 below. Preferably the TCM containsat least 1% by weight iron because the rate of production of TCM atlower iron contents becomes economically unattractive. The iron in TCMgenerally is not elemental iron, and usually is in the form of carbidesand/or oxides of iron. At least a portion of the iron of the "asproduced" TCM can be removed therefrom such as by leaching with an acid.Therefore the "as used" TCM can have an iron content of less than 0.1%by weight.

The TCM can also contain hydrogen such as when the feed gas used to formthe TCM contains hydrogen. Typically the TCM comprises from about 1 toabout 5% by weight iron, about 93.5 to about 99% by weight carbon, andup to about 1.5% by weight hydrogen. The iron content of TCM can bedetermined by burning off the hydrogen and carbon and assuming theremaining ash consists of Fe₂ O₃. FIGS. 1 and 2 show a transmissionelectron micrograph and a scanning electron microscope photograph,respectively, of TCM. From such micrographs and photographs it has beendetermined that TCM comprises intertwined tendrils having a diameter(number average) of from about 0.05 to about 0.2 micron and a length(number average) to diameter (number average) ratio greater than about10.

Surprisingly, as shown in FIG. 3, for one form of TCM, there is apositive correlation between the surface area of TCM and its bulkdensity, i.e. the surface area of TCM increases as its bulk densityincreases. As used herein, all the surface area values of TCM presentedare obtained by the BET method of Brunnauer, Emmett, and Teller, J. Am.Chem. Soc., 60, 309 (1938). The reproducibility of the specific surfacearea measurement on different samples of the same batch of "as prepared"TCM using this method is typically about ±7%, while the reproducibilityof the measurement on the same sample is typically ±2 to 3%. Preferablythe surface area of TCM is less than 190 m² /g, and more preferably lessthan about 160 m² /g for the TCM to have the ultra low bulk densityrequired for TCM to be an effective viscosifier. Typically TCM has asurface area greater than about 30 m² /g, and preferably from about 50to about 160 m² /g.

The novel material of the present invention has now been characterizedin five ways:

1. Its chemical composition, and particularly the amount of iron presentin the "as formed" material;

2. Bulk density;

3. Surface area;

4. Tendril diameter; and

5. Tendril length to diameter ratio.

A theory for the fact that carbonaceous materials having a bulk densityof greater than about 0.1 g/cm³ and a surface area greater than about190 m² /g are ineffective as viscosifiers is available. Not to be boundby this theory, it is believed that in a high bulk density material thetendrils are knit together and there is material of varying densityinterspersed between the tendrils. This is shown by transmissionelectron microscope photographs. It is believed that in the high densitymaterial with high surface area the tendrils are so tightly boundtogether by the inter-knitting that the tendrils cannot interlockthroughout a liquid and hence do not produce gelling. In short, thetightly bound fibrous material acts as individual particles that havelittle interaction with each other and hence do not set up a fibermatrix throughout the liquid.

Contrarily, with the low bulk density, lower surface area material thetendrils interact with each other to produce the matrix effect neededfor increasing viscosity of a liquid and for gelling a liquid.

B. Methods for Producing TCM

Three methods will be described for producing TCM: (1) a fixed bedmethod for producing small quantities of starter material; (2) a fixedbed method for producing large quantities of TCM; and (3) a fluidizedbed method for producing large quantities of TCM. All three methods havecertain features in common, namely:

1. The TCM is formed by disproportionation of carbon monoxide in thepresence of an iron containing particulate;

2. The particulate is finely divided, preferably having a number averagediameter of less than about 10 microns, and most preferably less thanabout 2 microns;

3. The temperature at which disproportionation occurs must be controlledwithin a narrow temperature range, about 400° to about 500° C.,preferably from about 430° to about 460° C. for a fixed bed process, andpreferably from about 450° to about 490° C. for a fluidized bed process;and

4. Sufficient room in the bed is provided that the particulate can bedilutely dispersed and the carbon tendrils can grow in an unrestrainedfashion.

It has been found that processes not satisfying these requirements failto produce the desired ultra low bulk density material. For example, attemperatures greater than about 500° C., the material formed has ahigher bulk density and larger fiber diameters than desired and isunsatisfactory as a viscosifier. This is demonstrated by Examples 4, 15and 16 below. At temperatures below about 400° C. there is a potentialfor formation of Fischer-Tropsch waxes.

If the reactor bed is restrained, the product formed has a higher bulkdensity than desired. It is necessary to have the growing fiber massexpand outwardly rather than grow inwardly or densify. This isdemonstrated by Example 5 below. Similarly if the iron containingparticles are too close together in the bed a product with a bulkdensity higher than about 0.1 g/cm³ is formed. This is demonstrated byExample 1 below.

The particulate containing iron can comprise only an iron compound. Forexample, the particulate can be iron oxide powder (Fe₂ O₃) with a numberaverage particle size of 0.5 micron. Other iron oxides such as Fe₃ O₄ orfinely divided iron powders such as carbonyl iron or iron metal can beused. All particles sizes for the particulate presented herein arenumber average.

It is believed that other forms of iron can be used, including alloys ofiron. However, an attempt to make TCM according to the present inventionwith stainless steel as the disproportionation catalyst wasunsuccessful. The iron containing catalyst can be promoted withdisproportionation promoters, such as alkali metal hydroxides, includingsodium hydroxide and potassium hydroxide. It is believed that "ferrousmetals" other than iron can be used. By the term "ferrous metal" thereis meant metals of Group VIII of the Periodic Table of the Elements,including iron, cobalt, nickel, and combinations, carbides, oxides, andalloys thereof.

The feed gas used is a gas mixture whose reactive components are carbonmonoxide and hydrogen. When made conventionally, as in coalgasification, such gas mixtures generally also contain non-reactivecomponents such as nitrogen. Most commercially available gas feedstreams containing carbon monoxide also contain relatively large amountsof hydrogen. Production of TCM is generally effected with feed gasstreams having carbon monoxide to hydrogen molar ratios of at leastabout 1:1, preferably at least about 2:1, and generally up to about10:1.

In the method for manufacturing small quantities of TCM, the particulatecontaining iron is spread in a thin layer on a substrate such as aquartz plate that is then placed in a reactor which can be a horizontaltubular reactor. Preferably the layer is very thin. For example, for aparticulate consisting of iron oxide powder, Fe₂ O₃, having a particlesize of about 0.5 micron, preferably the thickness of the particulatelayer is less than about 0.01 gram of iron per square centimeter. Theimportance of using a thin layer is demonstrated by Example 1 below.

The feed gas is passed over the iron powder at a temperature of fromabout 400° to about 500° C. and the iron of the particulate catalyzesthe disproportionation of at least a portion of the carbon monoxide toform TCM.

Carbon deposition rates for a feed gas consisting of 52% carbon monoxideand 48% hydrogen are typically from about 1 to about 2 pounds of carbonper hour per pound of iron. This rate is increased by about 30% if theiron oxide powder is promoted with 0.75 weight percent sodium hydroxide,based on the weight of the iron oxide.

Since sulfur compounds can poison the iron containing catalyst, theypreferably are removed from the feed gas. Good results have beenobtained with iron oxide powder containing less than 0.1% by weightsulfur.

Although this first method is effective for producing ultra low bulkdensity TCM, it is unsatisfactory for commercial production. The secondmethod, which also uses a fixed bed, is better for producing largequantities of TCM. In this method the iron catalyst is made sufficientlydilute by blending it into already prepared TCM. The TCM used can bethat formed by the first method. The intertwined carbon tendrils of theTCM entrap and disperse the catalyst particles and keep individualparticles separated into a three dimensional matrix. Using the combinedTCM/particulate starting mass, addition of carbon occurs by expandingthe volume of the mass rather than by increasing the density of themass. It is possible to add at least 10 times or more to the amount ofcarbon in the original TCM mixture.

A blend of TCM and the particulate containing iron can be obtained bydry blending the two materials in a vee type blender. Alternatively,blending can be effected by mixing the two powders in an organic liquidsuch as toluene, filtering the mixed solid mass, and drying.

The ratio of the mass of iron to the mass of TCM in the blend is atleast about 1:20 to obtain effective rates of production and can be upto about 4:1.

In the third method, rather than using the blend in a fixed bed, theblend is used in a fluidized bed. Techniques for manufacturing fibrouscarbonaceous material in a fluidized bed are described in aforementionedU.S. patent application Ser. No. 620,996 filed June 15, 1984 by EdwardF. Brooks. A difference between the process of the present invention andthe process described in the '996 application is that in the process ofthe present invention no abradant is used in the fluidized bed.

In the fluidized bed method the same feed gas can be used as is used inthe fixed bed method. However, the blend of TCM and particulatecontaining iron contains no more than about 40% by weight iron, andpreferably less than about 20% by weight iron, to avoid forming acarbonaceous material having a bulk density too high to be effective asa viscosifier.

The blend of the TCM and particulate containing iron are fluidized bythe feed gas, with the feed gas being introduced at a superficialvelocity sufficient to fluidize the bed. The superficial velocity of thefeed gas is from about 3 to about 20 cm/sec, and preferably from about 6to about 15 cm/sec.

The reactor operating pressure can be from about 1 to about 10atmospheres. The contact time of carbon monoxide with particulatecontaining iron is from about 10 to about 100 seconds, more preferablyfrom about 30 to about 80 seconds.

For the fluidized bed method, preferably the feed gas inlet temperatureis at least about 50° C. lower than the reactor temperature whenproducing commercial quantities of TCM. Generally the feed gas inlettemperature is less than about 300° C., and preferably less than about250° C., for three reasons: (i) to avoid deposition of carbon upstreamof the reaction zone which can occur at high temperatures; (ii) to avoidlocal over-heating at the reaction zone entrance; and (iii) to helpremove heat of reaction in the vicinity of the reaction zone entrance.The disproportionation reaction is exothermic, and cooling can berequired.

C. Representative Applications for TCM

TCM has many important applications. TCM is particularly effective forincreasing the viscosity and for gelling a wide range of materials.Liquids whose viscosity can be increased and that can be converted tonon-pourable gels at room temperature by addition of small amounts ofTCM are presented in Table 1. By the term "gel" there is meant that atroom temperature the composition has a viscosity greater than 100,000cps and cannot be poured. With reference to Table 1, the water with a pHof 3.0 was produced by adding sulfuric acid to the water. The watersamples having a pH of 9.5 and 12 were prepared by adding sodiumhydroxide to water.

To increase the viscosity of a liquid with TCM it is merely necessary todisperse the TCM in the liquid such as with a Waring blender. Wettingagents generally are not required. When producing mixtures of TCM withaqueous solutions containing high concentrations of electrolytes such ascalcium chloride, it is more effective to first add the TCM to the waterbefore dissolving the salt.

Generally at least 0.1% by weight TCM is added to the liquid. SufficientTCM is added to satisfy one or both of the criteria that (1) theviscosity of the liquid is increased by at least a factor of 10 and (2)the viscosity of the liquid is at least 10 cp at a shear rate of 1sec⁻¹.

                  TABLE 1                                                         ______________________________________                                        Gels Formed With TCM                                                                                TCM Content                                             Liquid                (% by Wt)                                               ______________________________________                                        Distilled Water       5-8                                                     pH 3.0 Water          5                                                       pH 9.5 Water          5                                                       pH 12 Water           5                                                       Saturated Calcium Chloride Solution                                                                 5                                                       10% Potassium Chloride Solution                                                                     5                                                       20% Potassium Chloride Solution                                                                     5                                                       Distilled Kerosene    10                                                      Mobil Lubirte ™  Motor Oil                                                                       9.5                                                     Methanol              8.7                                                     Mineral Oil           6                                                       n-hexane              5                                                       JP-5 Fuel             7                                                       Base Oil for Commercial Calcium Grease                                                              8.5                                                     Dow Corning Silicone Oil                                                                            8                                                       ______________________________________                                    

When percent by weights of TCM in a liquid are presented herein, thereis meant the percent by weight of the total composition, i.e. the liquidin combination with the TCM and any other additives present. Forexample, a mixture of 5 grams of TCM, 15 grams of barite, and 80 ml ofwater contains 5% by weight TCM.

Table 1 demonstrates that TCM can be used to thicken silicone oils,hydrocarbons, and aqueous solutions, including aqueous solutions havinglow and high pH's and aqueous solutions containing electrolytes. This isunusual, particularly in that a wetting agent is not needed. Othercommon viscosifiers such as clays or fumed silicas require specialtreatments or wetting agents in order to broaden their range ofapplicability. Also other common viscosifiers are not effective withboth acidic and basic solutions. For example, fumed silicas, whichdepend on hydrogen bonding to establish a long range gelling matrix, areessentially ineffective in high pH solutions as demonstrated by Example7 below.

When TCM is added to liquids, the resulting mixture is highly shearthinning, i.e. as the shearing rate on the material is increased, forexample by stirring or pumping, the effective viscosity decreases (seeExample 7). However, unlike many other gelling materials such as fumedsilicas and clays, the viscosity at any shear rate does not change withtime (see Example 8). Particularly at low shear rates, the viscosity ofmixtures of TCM with liquids is generally much more independent oftemperature than is the base liquid (see Example 9). A glob of gel madeby adding 8% TCM to mineral oil showed no slumping, melting,liquid-solid separation, or visible deformation when heated from 22° to135° C. Over that temperature range the viscosity of the base mineraloil changed by about a factor of 30. This temperature stability of TCMis in sharp contrast to polymeric viscosifiers which generally start tobreak down at temperatures of 125° to 150° C. A diesel oil, with only 3%by weight addition of TCM, was very stable in a 72 hour rolling test at150° C. (see Example 10).

Not only is TCM an effective, temperature stable viscosifier, it is alsoable to hold in suspension other denser, solid particles that normallysettle to the bottom of an unstirred liquid. For example, it was foundthat in water of pH 9.5, 7.5 pounds per barrel of TCM hold in suspensionindefinitely 400 pounds per barrel of very dense, 4.5 g/cm³ barite.

One use of TCM as a viscosifier is to blend it with lubricating oils toproduce thermally stable lubricating greases. Such a grease comprises alubricating oil having dispersed therein sufficient TCM, in an amount ofat least 0.1% by weight of the grease, that the grease has an apparentviscosity of at least 4 Pa·S at a shear rate of 100 sec⁻¹. Allviscosities presented herein, unless indicated otherwise, are thosemeasured at room temperature. Surprisingly it was found that theaddition of TCM to a base lubricating oil produces a grease with a lowercoefficient of friction than the base oil itself in elastohydrodynamiclubrication. "Elastohydrodynamic lubrication" refers to the lubricationof highly loaded machine elements such as gears, cams, and rollingelement bearings, where two opposing surfaces are either completely orin part separated by just a lubricant film.

In addition, TCM added to water in a sufficient quantity to gel thewater has a lubricating effect (see Example 13 below). Such water basedgels containing TCM can make good cutting or machining lubricants and/orlubricants for high temperature forging or extrusion.

A wide variety of lubricating oils, including silicone oils, can be usedin greases according to the present invention. Lubricating oils have aviscosity in the range of 25 mm² /S to 650 mm² /S at 40° C. can be used.Generally petroleum oils of about 100 to 130 mm² /S viscosity at 40° C.are used to form the grease. The base oil need not be natural petroleumoil, but can be a synthetic oil such as a diester or a silicone oil.

In addition to TCM, other thickeners or gelling agents can be used,including the fatty-acid soaps of lithium, calcium, sodium, aluminum,and barium. Also finely divided clay particles such as those of thebentonite and hectorite types, after coating with organic materials suchas quaternary ammonium compounds, can be used.

The grease can also contain chemical additives to improve oxidationresistance, provide rust protection, and provide the grease with extremepressure properties. For example 1-naphthyl(phenyl)amine can be added asan oxidation inhibitor.

The grease can contain additives to prevent water and salt-spraycorrosion such as amine salts, metal sulfonates, and cycloparaffinsalts.

TCM can also be used in a lubricating oil, preferably in an amount of atleast 0.1% by weight as a viscosity index improver. The base lubricatingoil can be any of those identified above as used for greases, includingpetroleum oils, synthetic hydrocarbon oils, and silicone oils. Thelubricating oil can contain additives in addition to TCM, such asoxidation inhibitors including hindered phenols and amines. Thelubricating oil can also contain rust inhibitors such as mildly polarorganic acids, including those of the alkyl-succinic type. Thelubricating oil can also contain anti-wear agents, detergents,dispersants, pour-point depressants, and viscosity-index improvers inaddition to the TCM.

Another important application for TCM is in drilling fluids. Inwell-drilling operations, the drilling fluid or mud is pumped down ahollow drill string and down through drill bit nozzles in the bottom ofthe bore hole. From there the mud passes up to the surface through anannulus formed by the bore hole or casing and the drill string to bringformation cuttings to the surface. In drilling the well a drill bit isturned by rotating the drill string or by rotating the drill bit with adown hole motor. The drilling fluid, after it reaches the surface, hasformation material removed from it, and is then treated with additivesto obtain a set of desired properties. Once treated, the fluid is pumpedback into the well and the cycle is repeated.

It is desirable that the drilling fluid be thin at the drilling bitwhere the shear rate is very high and thicker in the return annulus inorder to carry away the formation cuttings. In the annulus area theshear rate is much lower than at the drill bit. Difficulty isexperienced in obtaining drilling fluids with these properties when thetemperature in the bore hole is very high, in the order of about 400°F., as is experienced with deep bore holes.

TCM is a surprisingly effective additive for drilling fluids. A drillingfluid according to the present invention comprises a liquid havingdispersed therein (i) sufficient weighting agent that the drilling fluidhas a density of at least 1.1 g/cm³ and often at least 1.5 g/cm, and(ii) sufficient TCM in an amount of at least 0.1% by weight that thedrilling fluid has a viscosity of at least 10 cp at room temperature ata shear rate of 1000 sec⁻¹. TCM not only provides the drilling fluidwith the desired viscosity, it also helps suspend the dense material.Water based drilling muds can be formulated with TCM to have thefollowing viscosities:

(1) in the drill bit area where shear rates can be greater than 10,000sec⁻¹, less than 10 cp; and

(2) in the annulus region where shear rates can be from 10 to 500 sec⁻¹,less than about 100 cp.

Sufficient TCM is used to suspend the weighting agent. For example, agel strength of 5 lb/100 ft² is adequate to suspend barite. TCM in awater based mud, (having a density of 15.5 lb/gal) gives a gel strengthgreater than 5 lb/100 ft².

TCM is effective in drilling fluids where the liquid is (1) water,including fresh water, sea water, and salt water; (2) hydrocarbon basedsuch as petroleum based; and (3) water-in-oil emulsions. As shown inTable 1 above, TCM is an effective viscosifier for both oil and watersystems, including water systems containing high concentrations ofelectrolytes. In addition, most water based drilling fluids arealkaline, having a pH of from about 9.5 to about 12 and TCM is effectivein alkaline solutions as shown by the data presented in Table 1 above.

The drilling fluid of the present invention contains sufficientweighting agents to provide hydrostatic pressure against exposedformations in excess of the pressure of the formation fluids. Inaddition, sufficient weighting agent is provided in the drilling fluidso the hydrostatic pressure of the column of drilling fluid preventscollapse of weak formations into the bore hole. The preferred densifyingmaterial is barite. Other densifying materials that can be used includegalena (PbS), natural and synthetic hematite (Fe₂ O₃), magnetite (Fe₃O₄), ilmenite (FeTiO₃), siderite (FeCO₃), celesite (SrSO₄), dolomite(CaCO₃.MgCO₃), and/or calcite (CaCO₃).

In addition to TCM, other viscosifiers can be used such as bentonite,attapulgite, and organophilic clays.

Organic polymers can be used to increase viscosity and to controlfiltration rates, including starch, guar gum, sodium carboxymethylcellulose, and xanthan gum. In some instances thinning agents such aslignosulfanate can be used.

As noted above water-based drilling fluids are generally maintained atan alkaline pH to function properly and to reduce corrosion. Sodiumhydroxide, lime, or magnesium oxide can be used for this purpose.

The drilling fluid can contain surfactants when the base liquid is awater-in-oil emulsion.

Other additives commonly used in conventional drilling fluids can beused in the drilling fluid.

The TCM, weighting agents, and other additives can be provided as a drymixture, or a mixture dispersed in a liquid at high concentrations, forlater dispersion in a liquid at desired concentrations to form adrilling mud.

EXAMPLES

These and other features of the present invention are demonstrated bythe following Examples.

EXAMPLE 1

This Example demonstrates that in the fixed bed method for producingsmall quantities of TCM the thickness of the layer of the ironcontaining particulate affects the bulk density of the product formed.

The catalyst used was iron oxide powder (Fe₂ O₃) having a number averageparticle size of 0.5 micron. The iron oxide powder was spread uniformlyover the bottom of a horizontal quartz reactor tube having a diameter of3 inches and a length of 3 feet. The catalyst was spread over only 9inches of the length of the tube. The reactor tube was placed in aLindburg furnace having a uniform hot zone about 18 inches long, withall the iron oxide powder in the uniform hot zone. Feed gas consistingof 50% carbon monoxide and 50% hydrogen was introduced into the reactortube at one end, preheated to reactor temperature, passed over the ironoxide powder, and then passed out the other end of the reactor tube. Thegas flow rate was 0.335 standard liters per minute. During the course ofthe run which lasted 24 hours, the temperature of the iron oxide powderwas controlled between about 427° and 441° C.

After 24 hours the resulting fibrous carbon mass was recovered. Threeruns were conducted at differing catalyst powder layer thicknesses.

The results of the three runs are presented in Table 2. The resultsindicate that to obtain a fibrous carbonaceous material having a bulkdensity of less than about 0.1 g/cm³ it is necessary that the catalystpowder layer thickness be less than about 0.01 gram Fe/cm².

EXAMPLE 2

This Example demonstrates the effectiveness of the use of a blend of TCMand iron oxide particulate for forming TCM.

In this Example, the same technique used for Example 1 was used, exceptthat 0.782 grams of iron oxide powder were dry blended with 3.128 gramsof previously prepared TCM. The resulting mixture contained 20% byweight of the iron oxide powder and about 2% by weight of other ironthat was in the previously prepared TCM. This blend was used in the samereactor with the same furnace with the same feed gas, the same gas flowrate, and the same temperatures as used for Example 1.

After 24 hours, the material present in the reactor was recovered. Thisrecovered material weighed 23.9 grams and contained 97.5% by weightcarbon.

                  TABLE 2                                                         ______________________________________                                        Effect of Iron Oxide Catalyst Powder Layer Thickness                          On The Resulting Bulk Density of Fibrous Carbon                                    Catalyst Powder            Product Bulk                                       Layer Thickness                                                                              Product Carbon                                                                            Density                                       Run  (Grams Fe/cm.sup.3)                                                                          (Weight %)  (Grams/cm.sup.3)                              ______________________________________                                        1    0.0026         97.6        0.044                                         2    0.0043         98.5        0.086                                         3    0.0124         97.8        0.11                                          ______________________________________                                    

The bulk density of the material was 0.030 g/cm³ and its surface areawas 138 m² /g.

The average carbon deposition rate was 1.54 grams of carbon per hour pergram of iron, and 15.6% of the carbon that was in the inlet gas (ascarbon monoxide) was deposited as fibrous carbon.

EXAMPLE 3

The procedure of Example 2 was repeated except that the blend contained50% by weight of the iron oxide powder and 50% by weight of thepreviously prepared TCM. The run was for 19.2 hours and the temperaturewas controlled between 421° and 428° C. The final carbon content of theformed TCM was 96% by weight, its bulk density was 0.027 g/cm³, itssurface area was 122 m² /g, and its number average fiber diameter was0.12 micron.

EXAMPLE 4

The procedure of Example 2 was repeated except that the temperature wasbetween 455° and 470° C. rather than 427° to 441° C. The TCM formedcontained 98.3% carbon and had a bulk density of 0.1 g/cm³. The averagecarbon deposition rate was 2.24 grams of carbon per hour per gram ofiron.

This Example demonstrates that at reaction temperatures approaching 500°C., the bulk density of the TCM begins to become higher than desired,i.e. becomes greater than about 0.1 g/cm³. Comparing the results of thisExample with the results of Example 2 shows that by increasing theaverage temperature by about 30° C. a product with over three timeshigher bulk density is formed.

EXAMPLE 5

This Example shows that restraining the growth of carbon fibersincreases the bulk density of the product formed.

In this Example the same procedure used for Example 2 was used exceptthat the blend of TCM and iron oxide powder was loaded into a 1"diameter by 12" long cylindrical quartz boat with closed ends. This boatwas then loaded into the 3" horizontal reactor tube described inExample 1. Thus the growing carbon mass was able to expand only in onedirection, i.e. up.

The final product contained 97.6% by weight carbon and had a bulkdensity of 0.072 g/cm³, which was over twice the bulk density of theproduct formed in Example 2 where the material was free to expand.

EXAMPLE 6

This Example shows the effect of increased catalyst particle size on thebulk density of the TCM formed.

The procedure of Example 2 was repeated except that carbonyl iron powderof mean particle the size of about 5 microns was substituted for the 0.5micron iron oxide catalyst. The carbonyl iron powder was dry blendedwith previously formed TCM in an amount sufficient that the blendcontained 20% by weight iron. During the run the temperature wasmaintained in the range of from 432° to 444° C. The final productcontained 96.6% by weight carbon and had a bulk density of 0.078 g/cm³which is about 150% greater than the bulk density of Example 2.

EXAMPLE 7

This Example demonstrates that TCM is effective as a viscosifier in bothacidic and basic solutions and is a more effective viscosifier thanfumed silica.

Standard aqueous solutions were made by adding sulfuric acid or sodiumhydroxide to distilled water to obtain solutions having a pH of 12, 9.5,and 3.0. The pH values were determined with a Corning model 12 researchpH meter. To 50 ml samples of each solution, there were added 2.63 gramsof TCM made by a fixed bed method using a blend of TCM and an ironcontaining catalyst. The TCM added to each solution had a bulk densityof 0.031 g/cm³, a surface area of 117 m² /g, a fiber length to diameterratio of greater than 10, and an iron content of 2.7% by weight. Themixtures were blended in a Waring mixer for one minute, sealed in glassbottles, rotated on a paint roller for 16 hours, and then the effectiveviscosity of the material was measured as a function of shear rate usinga Brookfield viscometer. In a Brookfield viscometer the solution to bemeasured is placed in a narrow annulus between a rotating bob and astationary cup. The shear force required to maintain the bob at aconstant rotational speed (or shear rate) is directly measured and theeffective viscosity is calculated from the shear force measurements, therate of rotation of the bob, and the geometry of the system.

Table 3 shows the effective viscosity as a function of shear rate forthe three sample mixtures For comparison purposes, the viscosity of thesame solutions containing 5% by weight grade M-5 Cab-O-Sil.sub.™ fumedsilica is shown at each of the 3 pH values and at a shear rate of 5sec⁻¹. Within a typical reproducibility of these measurements (±25%), pHclearly had no effect on the viscosifying effect of TCM. Contrarily,with the fumed silica material there is a very strong effect in that athigh pH values of 12 the fumed silica provided no thickening at all ofthe solution at the 5% by weight level.

The water solution without the carbon or silica added had a viscosity ofabout 1 cp.

The data in Table 3 demonstrate that TCM at a concentration of 5% byweight dramatically thickens water solutions. In acidic solutions it is10 times more effective than fumed silica, while in basic solutions itis 2 to 3 orders of magnitude more effective than fumed silica. Furtherwith TCM there is a pronounced shear thinning effect in that theeffective viscosity at a relatively stagnant shear rate of 0.5 sec⁻¹ isapproximately 40 times higher than the viscosity at a shear rate of 93sec⁻¹.

                                      TABLE 3                                     __________________________________________________________________________    Viscosity (cp) of Fibrous Carbon and Cab-O-Sil                                Fumed Silica in Acid and Basic Solutions                                      Shear Rate                                                                          pH 3 Solution                                                                        pH 9.5 Solution                                                                       pH 12 Solution                                                                        pH 3 Solution                                                                        pH 9.5 Solution                                                                       pH 12 Solution                    (Sec.sup.-1)                                                                        5% Carbon                                                                            5% Carbon                                                                             5% Carbon                                                                             5% Cab-O-Sil                                                                         5% Cab-O-Sil                                                                          5% Cab-O-Sil                      __________________________________________________________________________    0.5   20,500 16,600  18,600  --     --      --                                1.0   9,875  8,275   9,000   --     --      --                                5.0   2,925  1,760   2,220   200    100     1                                 19    600    655     850     --     --      --                                46    502    435     528     --     --      --                                93    422    542     411     --     --      --                                __________________________________________________________________________

EXAMPLE 8

This Example demonstrates that the effect of TCM on the viscosity ofmineral oil does not change appreciably with time.

TCM in an amount of 1.55 grams was added to 50 ml of mineral oil whichhad a viscosity of 150 cp at 22° C. The TCM used was the same as usedfor Example 7. The mixture was blended on a Waring mixer for one minute.The mixture was loaded into a Brookfield viscometer and its effectiveviscosity was measured at 100 RPM (93 sec⁻¹ shear rate). The viscometerwas turned off and the sample was allowed to sit for ten seconds. Aviscosity reading was then made at a shear rate of 2.3 sec⁻¹ (2.5 RPM).The motor was turned off again, this time for ten minutes, and the 2.5RPM viscosity measurement repeated. The motor was then turned off for 20minutes and the 2.5 RPM measurement repeated and then again for 30minutes with a repeat of the 2.5 RPM measurement. The results arepresented in Table 4.

The results presented in Table 4 show that in the time frame of 10seconds to 30 minutes, the viscosity at low shear rate of mineral oilcontaining TCM does not appreciably change as the stagnation timebetween measurements increases.

                  TABLE 4                                                         ______________________________________                                        Viscosity of 3% Fibrous Carbon-Mineral Oil                                    Mixture as a Function of Time                                                 Time at Rest                                                                  (Minutes)                                                                              RPM      Shear Rate (Sec.sup.-1)                                                                      Viscosity (cp)                               ______________________________________                                                 100      93              410                                         0.166    2.5      2.3            1220                                         10       2.5      2.3            1240                                         20       2.5      2.3            1300                                         30       2.5      2.3            1300                                         ______________________________________                                    

EXAMPLE 9

This Example demonstrates the effectiveness of TCM as a viscosifier forlight mineral oil.

TCM having the same properties as the TCM of Example 7 was added tolight mineral oil in an amount of 5% by weight. The mixture was blendedfor one minute in a Waring mixer and then viscosity measurements weremade with a Brookfield viscometer as a function of shear rate attemperatures of 22° C., 70° C., and 85° C. The viscosity measurements onthe neat mineral oil (i.e. no TCM addition) were also made at 22° C. and70° C. FIG. 4 presents the results.

The results presented in FIG. 4 show that at low shear rates theviscosity of the TCM-mineral oil mixture is much less dependent ontemperature than the base mineral oil itself. At higher shear rates,however, the temperature dependency approaches that of the base mineraloil. FIG. 8 also shows that the viscosity of the mineral oil/TCM blends,like the aqueous blends described in Example 7, are highly shearthinning at all three temperatures investigated. The base mineral oilbehaves as a Newtonian fluid and does not show viscosity dependence onshear rate.

EXAMPLE 10

This Example demonstrates the heat stability of TCM as a viscosifier forboth oil based and water based muds. It also demonstrates that TCM iseffective in suspending dense materials in both oil and water basedsystems.

To 258 ml of #2 diesel oil were added 400 grams of -325 mesh barite(barium sulfate) and 6.2 grams of TCM. To water there was added either(1) barite in an amount of 400 lb/barrel; (2) TCM in an amount of 1% byweight; (3) barite in an amount of 400 lb/barrel and TCM in an amount of1% by weight; or (4) barite in an amount of 400 lb/barrel and TCM in anamount of 3% by weight. These mixtures were blended on a Waring mixerfor one minute and then the effective viscosity of the mixtures wasmeasured at room temperature as a function of shear rate using a Fannmodel 29-B viscometer. The Fann viscometer is very similar to theBrookfield viscometer used in the previous Examples except that it iscapable of covering a broader shear rate range (5 to 1277 sec⁻¹).

After the initial viscosity versus shear rate measurements were made onthe samples, the samples were placed in a steel cylinder, which was thensealed. The sealed cylinder was then placed in an oven equipped with arolling device for rotating the cylinder and the samples within theoven. The samples were initially heated to 300° F. and then rotated inthe oven for 72 hours, while holding the sample at 300° F. After thisthermal aging, the cylinder and samples were cooled to room temperature,the samples removed from the cylinder, and the viscosity of the sampleswas again determined as a function of shear rate.

Table 5 compares the initial viscosity versus shear rate data for theaged and unaged oil based samples after 72 hours of 300° F. thermalexposure. FIG. 8 shows viscosity versus shear rate for the aged waterbased systems. The aged oil based materials had slightly higherviscosity than the initially prepared materials particularly at thelower shear rates. FIG. 8 shows the synergistic effect of barite and TCMin increasing the viscosity of water. It should be noted that changes ineffective viscosity of the order of a factor of two or less areconsidered to be relatively minor.

EXAMPLE 11

This Example demonstrates that it is important for TCM to have a bulkdensity of less than about 0.1 g/cm³ to be effective as a viscosifier.

Four different sample batches of fibrous carbons, all produced bydeposition from a carbon monoxide containing gas, using iron basedcatalysts, were prepared. The samples all had low final iron contents(ranging from 2.7 to 4.3%) and were prepared in ways which led to fourdifferent bulk densities and associated surface areas. Samples A and Bwere prepared in a fixed bed and Samples C and D were prepared in afluidized bed. A fifth sample batch, commercial Fast Extrusion Furnace(FEF) carbon black was used for comparison purposes.

                  TABLE 5                                                         ______________________________________                                        Fann Viscosity vs. Shear Rate for an "As Prepared"                            Diesel Oil/TCM/Barite Sample and for the                                      Same Sample After 300° F. Thermal Aging                                      Shear Rate  Initial    Viscosity After 72                               RPM   (Sec.sup.-1)                                                                              Viscosity (cp)                                                                           Hrs at 300° F. (cp)                       ______________________________________                                        750   1277         94        112                                              600   1022        111        131                                              300   511         --         222                                              200   341         248        306                                              100   170         420        555                                               80   136         510        671                                               40    68         952        1170                                              15    26         1900       2600                                              3     5          3400       6000                                             ______________________________________                                    

Mixtures of each carbon batch with pH 9.5 water were prepared at the 3%,5%, and 7% carbon level. Each sample was blended on a Waring mixer forone minute, sealed in glass jars, and rotated on paint mixer rollers for16 hours. Sample viscosity was then measured as a function of shear ratewith a Brookfield viscometer.

An identical matrix of sample mixtures was also prepared using mineraloil as the base liquid in place of pH 9.5 water. The samples wereprepared in the same way as the aqueous mixtures and viscosity versusshear rate measurements were made with the Brookfield viscometer.

Tables 6 and 7 present the viscosity of mineral oil and waterrespectively, for the four fibrous carbons and FEF carbon black, at ashear rate of 25 sec⁻¹. It is apparent from Tables 5 and 6 that the lowbulk density fibrous carbons (samples A and B, 0.031 and 0.050 bulkdensity, respectively) were more effective in increasing viscosity theneither of the higher density fibrous carbons (samples C and D) or theFEF carbon black. The effects are most pronounced at the higher carbonlevels and at lower shear rates. FIG. 6 shows plots of viscosity of themixture versus carbon content. FIG. 7 shows plots of viscosity versusmaterial surface area at a shear rate of 5 sec⁻¹ for the 5% carbon inmineral oil samples. These Figures show that the highest surface area(high bulk density) sample D is a factor of 26 times less effective as aviscosifier than the low surface area, low bulk density samples A and B.

                                      TABLE 6                                     __________________________________________________________________________    Effective Viscosity At a Shear Rate of 25 Sec.sup.-1                          (Mineral Oil)                                                                        Surface Area                                                                          Bulk Density Viscosity (cp)                                    Sample (Sq Meters/Gr)                                                                        (Grams/cm.sup.3)                                                                     3% Carbon                                                                           5% Carbon                                                                            7% Carbon                                  __________________________________________________________________________    A      117      0.031 485   2662   >10000                                     B      129      0.050 738   2685   >10000                                     C      192     0.15   283   325    604                                        D      247     0.25   210   254    301                                        FEF Carbon                                                                           --      0.25   236   319    416                                        Black                                                                         __________________________________________________________________________

                                      TABLE 7                                     __________________________________________________________________________    Effective Viscosity At a Shear Rate of 25 Sec.sup.-1                          (pH 9.5 Water)                                                                       Surface Area                                                                          Bulk Density Viscosity (cp)                                    Sample (Sq Meters/Gr)                                                                        (Grams/cm.sup.3)                                                                     3% Carbon                                                                           5% Carbon                                                                            7% Carbon                                  __________________________________________________________________________    A      117      0.031 111   581    2093                                       B      129      0.050 202   747    2705                                       C      192     0.15    14    49    79                                         D      247     0.25    2     10    --                                         FEF Carbon                                                                           --      0.25    3     8     30                                         Black                                                                         __________________________________________________________________________

FIG. 6 shows that the viscosity increases more rapidly with increasingcarbon content in mineral oil for the low surface area materials thanfor the high surface area materials or the FEF carbon black. FIG. 7shows that the shear thinning effect of 5% carbon in mineral oil is muchmore pronounced for the low bulk density carbons than for the high bulkdensity carbon. That is to say, the effective viscosity decreases morerapidly with increasing shear rate for TCM than for higher bulk densitycarbons. It is because of this property that the ultra low bulk densitymaterial of the present invention is an effective additive for greases.

EXAMPLE 12

This Example demonstrates the importance of maintaining the iron contentof TCM at less than about 5% by weight.

A sample of fibrous carbon material was prepared by deposition from acarbon monoxide containing gas stream over an iron catalyst in a fixedbed. The final iron content of the material was 10.2% by weight, itsbulk density was 0.050 grams/ml, and its surface area was 122 m² /g. Asecond sample of fibrous material was also prepared with an iron contentof 2.6% by weight, a bulk density of 0.050 g/cm³, and a surface area of129 m² /g in a fixed bed.

Each sample of fibrous carbon was mixed with mineral oil and blended forone minute in a Waring mixer. The mineral oil/carbon mixtures contained3% by weight of fibrous carbon. Viscosity versus shear rate measurementswere made with each of the mixtures at room temperature using theBrookfield viscometer.

Table 8 compares the viscosity versus shear rate results for the twocarbon/mineral oil mixtures. The only significant difference between thesamples is the iron content of the carbons (and by inference theirassociated fiber lengths). It is apparent that the carbon sample withlow iron content (longer fiber length) was significantly more effectivein thickening mineral oil than was the higher iron content material.This effect was most pronounced at low shear rates and the differencesbetween the two materials diminished as the shear rate increased.

EXAMPLE 13

Three materials were tested for their effectiveness as a grease. Thefirst material was a base oil, the second material was grease consistingof the base oil and 8.5% by weight TCM, and the third material was watercontaining 8.5% by weight TCM. The effectiveness of these materials as agrease was tested in an apparatus in which a crown roller was contactedagainst a flat disk at high pressure. The coefficient of friction of thematerials for various velocities of the crown roller at pressures of0.76 GPa and 1.0 GPa are presented in Table 9. The results presented inTable 9 indicate that under all of the conditions the coefficient offriction of the TCM-oil grease was lower than the coefficient offriction of the oil by itself.

                  TABLE 8                                                         ______________________________________                                        Viscosity vs. Shear Rate Measurements for Two                                 Carbon/Mineral Oil Samples Where the Carbons                                  Contain 2.6% Iron and 10.2% Iron Respectively                                                  3% Carbon     3% Carbon                                                       .050 Bulk Density                                                                           .050 Bulk Density                                    Shear Rate 129 m.sup.2 /g                                                                              122 m.sup.2 /g                                 RPM   (Sec.sup.-1)                                                                             2.6 Wt % Iron 10.2 Wt % Iron                                 ______________________________________                                        0.5   0.5        8000          1100                                           1.0   0.9        4600          750                                            2.5   2.3        2420          480                                            5.0   4.7        1570          400                                            10.0  9.3        1090          370                                            20.0  18.6        812          325                                            50.0  46.5        590          244                                            100.0 93.0        491          282                                            ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        Comparison of Coefficient of Friction of                                      Commercial Base Oil and Low Density Carbon Grease                             Made With the Base Oil and With Water                                                            Coefficient of                                                                Friction at a                                                                            Coefficient of                                            Velocity Pressure of                                                                              Friction at a                                   Material  (m/sec)  0.76 (GPa) Pressure of 1.0 (GPa)                           ______________________________________                                        Base Oil  0.6      .047       .054                                                      1.2      .043       .051                                                      1.8      .035       .049                                            TCM + Base                                                                              0.6      .033       .045                                            Oil (Grease)                                                                            1.2      .022       .037                                                      1.8      .016       .032                                            Water + TCM                                                                             0.6      .058       .035                                                      1.2      .050       .040                                                      1.8      .064       .045                                            ______________________________________                                    

The results obtained with the water based TCM gel were also excellent.The TCM-water grease had a lower coefficient of friction than pure waterby more than an order of magnitude.

EXAMPLE 14

This test demonstrates that a drilling fluid according to the presentinvention containing TCM and barite is particularly effective.

To #2 diesel oil there were added (1) varying quantities of TCM; (2) 400pounds per barrel of barite; or (3) both TCM and barite. The viscosityof the mixtures was measured and the results are presented in Table 10and FIG. 9. The viscosity of a mixture of barite and TCM in the #2diesel oil was much higher than the sum of the viscosity increasesproduced by barite alone or by the TCM alone. The addition of 400 poundsper barrel of barite or 2.8 pounds of TCM per barrel to #2 diesel oilresulted in a relatively low viscosity fluid. However, when bothmaterials were added to #2 diesel oil, the viscosity of the resultingfluid was more than 3 times greater than the sum of the viscosity of thefluids with the individual additives.

                  TABLE 10                                                        ______________________________________                                        Effect on Viscosity of #2 Diesel Oil of Adding Barite                         Alone, Carbon Alone, and Barite and Carbon Together                           Effective Viscosity - CP                                                      Shear 400 Lbs/Barrel                                                                            2.8 lbs/barrel                                                                           400 Lbs/Barrel Barite                            Rate  of Barite in                                                                              of TCM in  Plus 2.1 lbs/barrel TCM                          Sec.sup.-1                                                                          #2 Diesel Oil                                                                             #2 Diesel Oil                                                                            in #2 Diesel Oil                                 ______________________________________                                        1277  16          7           80                                              1022  16          8           95                                              511   16          6          147                                              341   18          6          197                                              170   24          9          345                                              136   26          8          423                                               68   38          15         787                                               26   80          --         1380                                              10   200         --         1900                                              5    300         --         2800                                             ______________________________________                                    

EXAMPLE 15

This example demonstrates a fluid bed technique for making low densityTCM suitable for use as a viscosifier.

A mixture of 400 grams of previously produced TCM and 72 grams of ironoxide powder (Fe₂ O₃) having a number average particle size of 0.5micron was fed to a 16 cm diameter fluid bed reactor. The reactor wasoperated at an average temperature of about 465° C., and a superficialgas velocity of 8.4 cm/s. The feed gas contained 53% carbon monoxide byvolume. The production run lasted 23 hours and 50 minutes. The totaloutput from the run was 1723 g of product with an average iron contentof 4.8%, an average bulk density of 0.030 g/cm³, and an average surfacearea of 114 m² /g. The product material was found to have goodviscosifier properties.

EXAMPLE 16

This example demonstrates a fluid bed technique which failed to producelow density TCM suitable for use as a viscosifier.

The solids feed and operating conditions were nearly identical to thosein Example 15, with the exception that the average reactor temperaturewas about 505° C. The production run lasted 13 hours, 30 minutes. Thetotal output from the run was 3290 g of product with an average ironcontent of about 2%. The product material had a lighter fraction ofabout 640 g with a bulk density of about 0.056 g/cm³, and a more densefraction of about 2650 g with a bulk density of about 0.525 g/cm³.Samples from each fraction were found to have poor viscosifierproperties, especially the higher density sample.

E. Advantages

As demonstrated in detail above, the composition of matter of thepresent invention has many advantages over prior art viscosifiers,gelling agents, and suspending agents. It is an effective viscosifierand gelling agent for a wide variety of materials. TCM can be used withhydrocarbon, silicone, and aqueous based liquids. It can be used withaqueous liquids containing high levels of electrolytes. It can be usedwith low pH and high pH aqueous solutions. It has high temperaturestability and high shear thinning properties. There is a synergisticeffect between TCM and barite in drilling muds. The addition of TCM to abase lubricating oil produces a grease with a very low coefficient offriction. This property is also evidenced when TCM is added to water insufficient quantities to form a gel.

This unique combination of properties of TCM renders it effective formany applications, including applications in lubricating oils, greases,and drilling fluids.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. Therefore the spirit and scope of the appended claims shouldnot be limited to the description of the preferred versions containedherein.

What is claimed is:
 1. A method for suspending a dense solid in aliquid, the density of the dense solid being greater than the density ofthe liquid, the method comprising the step of dispersing in the liquidtendrillar carbonaceous material in an amount of at least 0.1% by weightbased on the weight of the liquid and the tendrillar carbonaeousmaterial, the amount of tendrillar carbonaceous material beingsufficient for suspending the dense solid in the liquid, the tendrillarcarbonaceous material having a bulk density of less than about 0.1 g/cm³and comprising intertwined tendrils having a diameter (number average)of from about 0.05 to about 0.2 micron and a length (number average) todiameter (number average) ratio greater than about
 10. 2. The method ofclaim 1 in which the liquid comprises water.
 3. The method of claim 1 inwhich the liquid comprises a hydrocarbon.
 4. The method of claim 1 inwhich the tendrillar carbonaceous material has a bulk density of lessthan about 0.05 g/cm³.
 5. The method of claim 1 in which the tendrillarcarbonaceous material has a surface area of less than about 190 m² /g.6. The method of claim 1 in which the tendrils comprise carbon fibersand an iron metal component dispersed throughout the carbon fibers asnodules that are intimately associated with and at least partiallybonded to the carbon fibers.
 7. The method of claim 6 in which thetendrillar carbonaceous material comprises from about 0.1 to about 5%weight iron, about 93.5 to about 99.9% by weight carbon, and up to about1.5% by weight hydrogen
 8. A method for preparing a tendrillarcarbonaceous material having a low bulk density comprising the stepsof:(a) blending (i) feed tendrillar carbonaceous material having a bulkdensity of less than about 0.1 g/cm³ and comprising intertwined tendrilshaving a diameter (number average) of from about 0.05 to about 0.2micron and a length (number average) to diameter (number average) ratiogreater than about 10 with (ii) a finely divided particulate comprisingan iron compound, the blend containing at least about 5% by weight iron;(b) introducing a feed gas containing carbon monoxide into a reactionzone having a fixed bed comprising the blend, the iron of theparticulate catalyzing the disproportionation of at least a portion ofthe carbon monoxide to form tendrillar carbonaceous material; (c)maintaining the temperature in the reaction zone at from about 400° toabout 500° C.; and (d) recovering tendrillar carbonaceous material fromthe reaction zone, the recovered tendrillar carbonaceous material havinga bulk density of less than about 0.1 g/cm³ and comprising intertwinedtendrils having a diameter (number average) of from about 0.05 to about0.2 micron and a length (number average) to diameter (number average)ratio greater than about 10, wherein the tendrils of the recoveredtendrillar carbonaceous material comprise carbon fibers and an ironmetal component dispersed throughout the carbon fibers as nodules thatare intimately associated with and at least partially bonded to thecarbon tendrils, the recovered TCM comprising from about 1 to about 5%by weight iron and at least about 93.5% by weight carbon.
 9. The methodof claim 8 in which the step of maintaining the temperature comprisesmaintaining the temperature in the reaction zone from about 420° toabout 450° C.
 10. The method of claim 8 in which the finely dividedparticulate has a number average diameter of less than about 10 microns.11. The method of claim 10 in which the iron in the particulate is in aform selected from the group consisting of oxides of iron, elementaliron, and combinations thereof.
 12. The method of claim 8 in which theblend contains less than about 80% by weight iron.
 13. The method ofclaim 8 wherein the recovered tendrillar carbonaceous material has asurface less than about 190 m² /g.
 14. The method of claim 8 in whichthe recovered tendrillar carbonaceous material comprises up to about 5%by weight iron.
 15. The method of claim 14 in which the recoveredtendrillar carbonaceous material comprises at least about 1% by weightiron.
 16. The method of claim 15 in which the feed gas contains hydrogenand the recovered tendrillar carbonaceous material comprises from about1 to about 5% by weight iron, about 93.5 to about 99% by weight carbon,and up to about 1.5% by weight hydrogen.
 17. The method of claim 8 inwhich the particulate comprises a disproportionation promoter.
 18. Amethod for preparing a tendrillar carbonaceous material having a lowbulk density comprising the steps of:(a) blending (i) feed tendrillarcarbonaceous material having a bulk density of less than about 0.1 g/cm³and comprising intertwined tendrils having a diameter (number average)of from about 0.05 to about 0.2 micron and a length (number average) todiameter (number average) ratio greater than about 10 with (ii) a finelydivided particulate comprising iron, the blend containing from about 5to about 40% by weight iron; (b) introducing a feed gas containingcarbon monoxide into a reaction zone having a bed containing the blendto form a fluidized bed, the iron of the particulate catalyzing thedisproportionation of at least a portion of the carbon monoxide to formadditional tendrillar carbonaceous material; (c) maintaining thetemperature in the reaction zone at from about 400° to about 500° C.;and (d) recovering tendrillar carbonaceous material from the reactionzone, the recovered tendrillar carbonaceous material having a bulkdensity of less than about 0.1 g/cm³ and comprising intertwined tendrilshaving a diameter (number average) of from about 0.05 to about 0.2micron and a length (number average) to diameter (number average) ratiogreater than about 10, wherein the tendrils of the recovered tendrillarcarbonaceous material comprise carbon fibers and an iron metal componentdispersed throughout the carbon fibers as nodules that are intimatelyassociated with and at least partially bonded to the carbon tendrils,the recovered tendrillar carbonaceous material comprising from about 1to about 5% by weight iron and at least about 93.5% by weight carbon.19. The method of claim 18 in which feed gas is introduced into thereaction zone at a superficial velocity of from about 3 to about 20cm/sec.
 20. The method of claim 19 in which the feed gas is introducedinto the reaction zone at a superficial velocity of from about 6 toabout 15 cm/sec.
 21. The method of claim 18 wherein the finely dividedparticulate has a number average diameter of less than about 10 microns.22. The method of claim 18 in which the bed contains less than about 20%by weight iron.
 23. The method of claim 18 wherein the recoveredtendrillar carbonaceous material has a surface area less than about 190m² /g.
 24. The method of claim 18 in which the recovered tendrillarcarbonadeous material comprises up to about 5% by weight iron.
 25. Themethod of claim 18 in which the recovered tendrillar carbonaceousmaterial comprises at least about 1% by weight iron.
 26. The method ofclaim 25 in which the feed gas contains hydrogen and the recoveredtendrillar carbonaceous material comprises from about 1 to about 5% byweight iron, about 93.5 to about 99% by weight carbon, and up to about1.5% by weight hydrogen.
 27. The method of claim 18 in which the step ofmaintaining temperature comprises maintaining the temperature in thereactor zone from about 440° to about 480° C.
 28. The method of claim 18in which the fluidized bed contains less than about 0.2 pounds of ironper cubic foot.
 29. The method of claim 18 in which the particulatecomprises disproportionation promoter.
 30. Low bulk density tendrillarcarbonaceous material produced by the method of claim
 8. 31. Low bulkdensity tendrillar carbonaceous material produced by the method of 18.32. A composition of matter suitable for combining with a liquid to forma drilling fluid, the composition of matter comprising (a) a weightingagent having a specific gravity greater than the specific gravity of theliquid, and (b) tendrillar carbonaceous material having a bulk densityof less than about 0.1 g/cm³, and comprising intertwined tendrils havinga diameter (number average) of from about 0.05 to about 0.2 micron and alength (number average) to diameter (number average) ratio greater thanabout
 10. 33. The composition of matter of claim 32 in which thetendrillar carbonaceous material has a surface area of less than about190 m² /g.
 34. The composition of matter of claim 33 in which thetendrillar carbonaceous material has a surface area of from about 30 toabout 160 m² /g.
 35. The composition of matter of claim 32 wherein thetendrillar carbonacous material has a bulk density of less than about0.05 g/cm³.
 36. The composition of matter of claim 32 in which thetendrils comprise carbon fibers and an iron metal component dispersedthroughout the carbon fibers as nodules that are intimately associatedwith and at least partially bonded to the carbon fibers.
 37. Thecomposition of matter of claim 36 in which the tendrillar carbonaceousmaterial comprises from about 0.1 to about 5% by weight iron, about 93.5to about 99.9 by weight carbon, and up to about 1.5% by weight hydrogen.38. The composition of matter of claim 32 in the liquid comprises water.39. The composition of matter of claim 32 in which the liquid comprisesa hydrocarbon.
 40. The composition of matter of claim 32 in which theweighting agent is barium sulfate.
 41. The composition of matter ofclaim 32 comprising a viscosity increasing agent in addition to thetendrillar carbonaceous material.
 42. The composition of matter of claim41 in which the viscosity increasing agent comprises clay.
 43. Thecomposition of matter of claim 32 comprising a viscosity thinning agent.44. The composition of matter of claim 32 comprising an alkalinitycontrol agent to maintain the pH of the drilling fluid greater than 7.0.45. The composition of matter of claim 32 comprising a flocculent.